Injection molding device with outside air inlet part

ABSTRACT

A resin molding device, resin molding method and resin molded product capable of guiding a sink to an optional position to perform a precise molding. A resin molding metal mold includes a gate formed in the central part of a cavity, a stepped part increasing the opening diameter of the cavity in the circumferential direction orthogonal to the flowing direction of a molten resin introduced into the cavity from the gate, and a fine outside air inlet part circumferentially formed on the outer part from the stepped part. The outside air inlet part is formed of a porous material and allowed to communicate with the outside of the resin molding metal mold through a communicating passage. Accordingly, the molten resin injected into the cavity from the gate is cooled with the outside air introduced from the outside air inlet part formed in the area except a transfer part after the reduction in resin pressure by the stepped part to generate a sink, forming a non-transfer part, so that the transfer property of the transfer part can be improved to enhance the shape precision of the molded product.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority under 35 U.S.C.§120 to U.S. application Ser. No. 10/003,283, filed Dec. 6, 2001 nowU.S. Pat. No. 6,918,752 and is also based upon and claims priority under35 U.S.C. §119 from Japanese Patent Application No. 2000-372870, filedDec. 7, 2000, the entire contents of each of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a resin molding device, resin molding methodand resin molded product, more specifically, a resin molding device,resin molding method and resin molded product capable of guiding a sinkto an optional place to perform a precise molding.

2. Description of the Prior Art

In an optical writing optical system such as laser type digital copyingmachine, laser printer, facsimile device or the like, an optical elementsuch as laser beam imaging rectangular lens or mirror having variouscorrecting apparatuses or the like is used.

In recent years, such an optical element is changed in material fromglass to plastic due to the demand for lower cost of product andvariously diversified in shape as thick wall, thin wall, longitudinallyuniform wall and non-uniform wall lenses according to required opticalperformances.

In resin molding, it is generally difficult to precisely arm a moldedproduct having a thick wall part or non-uniform wall part, and a failurephenomenon of transfer precision by sink or contraction distribution isapt to occur in a part requiring functional precision or a partrequiring transfer of fine surface shape.

Therefore, it was proposed in the past to press the reverse side orvicinity of a resin part requiring transfer precision to a transfersurface side by the pressure of fluid or gas in molding (refer toJapanese Patent Application Laid-Open No. 10-156861).

However, this method requires a high-pressure fluid EURO and anexpensive and complicated facility such as a control device forcontrolling the pressure and introducing timing of the fluid from thehigh-pressure source or the like because the reverse side or vicinity ofthe resin part requiring transfer precision is pressed to the transfersurface side by the pressure of fluid or gas, and also has the problemof poor availability in the use of a pressure-gas as the fluid, whichhas many restriction items up to the introduction of the facilityincluding the necessity of permissions for the use of high-pressure gas,the setting position of device and the like.

SUMMARY OF THE INVENTION

A first object of this invention is to provide a durable resin moldingdevice for molding a molded product by injecting a molten resin into thecavity of a metal mold followed by solidification, which comprises anoutside air inlet part formed on the metal mold and opened to anoptional part of the cavity to allow the outside of the metal mold tothe cavity inside and a stepped part formed within the cavity of themetal mold orthogonally to the flowing direction of the molten resincarried into the cavity, whereby the outside air inlet part can beformed in an optional part except a transfer surface to selectivelygenerate a sink in the resin of the outside air inlet part portion, andthe generation of sink in the surface subjected to transfer can beprevented in a low-pressure molding condition without using any specialor expensive device to mold a molded product having a highly precisetransfer surface at a low cost with low energy consumption.

A second object of this invention is to provide a durable resin moldingdevice for molding a resin molded product by injecting a molten resininto the cavity of a metal mold followed by solidification, whichcomprises a slit formed on the metal mold to allow an optional part ofthe cavity to communicate with the outside of the metal mold and astepped part formed within the cavity of the metal mold orthogonally tothe flowing direction of the molten resin introduced into the cavity,whereby the slit can be formed in an optional part except a transfersurface to selectively generate a sink in the resin of the slit part,and the generation of sink in the surface subjected to transfer can beprevented in a low-pressure molding condition without using any specialor expensive device to mold a molded product having a precise transfersurface at a lower cost with lower energy consumption.

A third object of this invention is to provide a resin molding device inwhich the outside air inlet part or slit is formed in the stepped partor the boundary of steps of the stepped part, whereby the stepped partand the outside air inlet part or slit can be formed in an optional partexcept the transfer surface to selectively generate the sink in thestepped part having the outside air inlet part or slit formed thereon,and the generation of sink in the surface subjected to transfer can bemore effectively prevented to mold a molded product having a moreprecise transfer surface.

A fourth object of this invention is to provide a resin molding devicein which the stepped part is formed so as to have a plurality ofcontinuous steps, whereby the sink can be more widely generated in thenon-transfer part to more effectively prevent the generation of sink inthe surface subjected to transfer, and a molded product having a moreprecise transfer surface can be molded.

A fifth object of this invention is to provide a resin molding device inwhich the stepped part is formed so as to have a plurality of continuoussteps, and the outside air inlet part or slit is formed in the statecommunicating with the cavity in the area between the steps, whereby thesink can be more widely generated in the non-transfer part to moreeffectively prevent the generation of sink in the surface subjected totransfer, and a molded product having a more precise transfer surfacecan be molded.

A sixth object of this invention to provide a resin molding device inwhich a gas feeding means for forcedly feeding a prescribed gas to theoutside air inlet part or slit is connected to feed the gas into thecavity through the outside air inlet part or slit by the gas feedingmeans during and after the injection of the molten resin into thecavity, whereby the timing of sink generation can be hastened to moreeffectively prevent the generation of sink in the surface subjected totransfer in the transfer of the surface of a part slightly distant fromthe sink position or the like, and the cooling can be rapidly progressedto mold a molded product, even if relatively thin, having a more precisetransfer surface.

A seventh object of this invention is to provide a resin molding devicein which the gas feeding means for forcedly feeding a prescribed gas tothe outside air inlet part or slit is connected to feed the gas into thecavity through the outside air inlet part or slit by the gas feedingmeans after the injection of the molten resin into the cavity, wherebythe resin surface in the periphery of the outside air inlet part or slitcan be separated from the metal mold surface while suppressing theentrainment of gas by the resin to guide the sink to an optionalposition, the timing of sink generation can be hastened to moreeffectively prevent the generation of sink in the surface subjected totransfer in the transfer of the surface of a part slightly distant fromthe sink position or the like, and the cooling can be rapidly progressedto mold a molded product, even if relatively thin, having a more precisetransfer surface.

An eighth object of this invention is to provide a resin molding methodfor molding a resin molded product by injecting a molten resin into thecavity of a metal mold followed by solidification, which comprisesinjecting the molten resin in the state it climbs over a stepped partformed within the cavity of the metal mold orthogonally to the flowingdirection of the molten resin introduced into the cavity whileintroducing the outside air into the cavity through a prescribed outsideair inlet part formed on the metal mold and opened to an optional partof the cavity to allow the outside of the metal mold to communicate withthe cavity inside, whereby a sink can be selectively generated in theresin of the outside air inlet part formed in an optional part exceptthe transfer surface to prevent the generation of sink in the surfacesubjected to transfer in a low-pressure molding condition without usingany special or expensive device, and a molded product having a precisetransfer surface can be molded at a low cost with low energyconsumption.

A ninth object of this invention is to provide a resin molding methodfor molding a resin molded product by injecting a molten resin into thecavity of a metal mold followed by solidification, which comprisesinjecting the molten resin in the state where it climbs over a steppedpart formed within the cavity of the metal mold orthogonally to theflowing direction of the molten resin introduced into the cavity whileintroducing the outside air into the cavity through a slit formed on themetal mold to allow an optional part of the cavity to communicate withthe outside of the metal mold, whereby a sink can be selectivelygenerated in the resin of the slit part formed in an optional partexcept the transfer surface to prevent the generation of sink in thesurface subjected to transfer in a low-pressure molding conditionwithout using any special or expensive device, and a molded producthaving a precise transfer surface can be molded by use of the cavityprecisely formed without providing any limitation to the metal moldmember at a lower cost with lower energy consumption.

A tenth object of this invention is to provide a resin molding method inwhich the outside air inlet part or slit is formed in the stepped partor the boundary of steps of the stepped part, whereby the stepped partand the outside air inlet part or slit can be formed in an optional partexcept the transfer surface to selectively generate the sink in thestepped part having the outside air inlet part or slit formed thereon,and the generation of sink in the surface subjected to transfer can bemore effectively prevented to mold a molded product having a moreprecise transfer surface.

An eleventh object of this invention is to provide a resin moldingmethod in which the stepped part is formed so as to have a plurality ofcontinuous steps, whereby the sink can be more widely generated in thenon-transfer part to more effectively prevent the generation of sink inthe surface subjected to transfer, and a molded product having a moreprecise transfer surface can be molded.

A twelfth object of this invention is to provide a resin molding methodin which the stepped part is formed so as to have a plurality ofcontinuous steps, and the outside air inlet part or slit is formed inthe state communicating with the cavity in the area between the steps,whereby the sink can be more widely generated in the non-transfer partto more effectively prevent the generation of sink in the surfacesubjected to transfer, and a molded product having a more precisetransfer surface can be molded.

A thirteenth object of this invention is to provide a resin moldingmethod in which a prescribed gas is fed into the cavity through theoutside air inlet part or slit by a gas feeding means for forcedlyfeeding the gas to the outside air inlet part or slit during and afterthe injection of the molten resin into the cavity, whereby the timing ofsink generation can be hastened to more effectively prevent thegeneration of sink in the surface subjected to transfer in the transferof the surface of a part slightly distant from the sink position or thelike, and the cooling can be rapidly progressed to mold a moldedproduct, even if relatively thin, having a more precise transfersurface.

A fourteenth object of this invention is to provide a resin moldingmethod in which a prescribed gas is fed into the cavity through theoutside air inlet part or slit by a gas feeding means for forcedlyfeeding the gas to the outside air inlet part or slit after theinjection of the molten resin into the cavity, whereby the resin surfacein the periphery of the outside air inlet part or slit can be separatedfrom the metal mold surface to guide the sink to an optional positionwhile suppressing the entrainment of gas by the resin, the timing ofsink generation can be hastened to more effectively prevent thegeneration of sink in the surface subjected to transfer in the transferof the surface of a part slightly distant from the sink position or thelike, and the cooling can be rapidly progressed to mold a moldedproduct, even if relatively thin, having a more precise transfersurface.

A fifteenth object of this invention is to provide a resin moldedproduct enhanced in the transfer property of the transfer surface near anon-transfer part to provide a precise transfer surface by forming theresin molded product by use of a resin molding device described in anyone of the first, second, fourth, sixth and seventh objects or accordingto a resin molding method described in any one of the eighth, ninth,eleventh, thirteenth, and fourteenth objects, and forming thenon-transfer part on the outside air inlet part or slit part.

A sixteenth object of this invention is to provide a resin moldedproduct enhanced in the transfer property of the transfer surface near anon-transfer part to provide a precise transfer surface by forming theresin molded product by use of a resin molding device described ineither of the third and fifth objects or according to a resin moldingmethod described in either of the tenth and twelfth objects, and formingthe non-transfer part in the stepped part or the boundary of steps ofthe stepped part.

A seventeenth object of this invention is to provide a resin moldedproduct enhanced in the transfer property of a tooth part that is anirregular-shaped power transmission part to provide a precise gear shapeby using a metal mold having a tooth part recessed part for molding thetooth part of a gear formed within the cavity on the moltenresin-flowing directional downstream side from the stepped part as themetal mold, forming the resin molded product by use of a resin moldingdevice described in any one of the first object to the seventh object oraccording to a resin molding method described in any one of the eighthobject to the fourteenth object, and form the tooth part.

In order to attain the above objects, a resin molding device for moldinga resin molded product by injecting a molten resin into the cavityfollowed by solidification according the first object comprises anoutside air inlet part formed on the metal mold and opened to anoptional part of the cavity of the metal mold to allow the outside ofthe metal mold to communicate with the cavity inside and a stepped partformed within the cavity of the metal mold orthogonally to the flowingdirection of the molten resin injected into the cavity.

In this structure, since the outside air inlet part opened to theoptional part of the cavity to allow the outside of the metal mold tocommunicate with the cavity inside is formed on the metal mold in themolding of the resin molded product by injecting the molten resin intothe cavity of the metal mold followed by solidification, and the steppedpart is formed within the cavity of the metal mold orthogonally to theflowing direction of the molten resin injected into the cavity, theoutside air inlet part can be formed in an optional part except atransfer surface to selectively generate a sink in the resin of theoutside air inlet part portion, and the generation of sink in thesurface subjected to transfer can be prevented in a low-pressure moldingcondition without using any special or expensive device to mold a moldedproduct having a precise transfer surface at a low cost with low energyconsumption.

A resin molding device for molding a resin molded product by injecting amolten resin into the cavity of a metal mold followed by solidificationaccording to the second object comprises a slit formed on the metal moldto allow an optional part of the cavity to communicate with the outsideof the metal mold and a stepped part formed within the cavity of themetal mold orthogonally to the flowing direction of the molten resinintroduced into the cavity.

In this structure, since the slit allowing the optional part of thecavity to communicate with the outside of the metal mold is formed onthe metal mold, in the molding of the resin molded product by inject themolten resin into the cavity of the metal mold followed bysolidification, and the stepped part is formed within the cavity of themetal mold orthogonally to the flowing direction of the molten resininjected into the cavity, the slit can be formed in an optional partexcept the transfer surface to selectively generate a sink in the resinof the slit part, and the generation of sink in the surface subjected totransfer can be prevented in a low-pressure molding condition withoutusing any special or expensive device to mold a molded product having aprecise transfer surface at a lower cost with lower energy consumptionby use of the cavity precisely formed without providing any limitationto the metal mold member.

In each case, for example, the outside air inlet part or slit may beformed in the stepped part or the boundary of steps of the stepped partas described in the third object.

In the above structure, since the outside air inlet part or slit isformed in the stepped part or the boundary of steps of the stepped part,the stepped part and the outside inlet part or slit can be formed in anoptional part except the transfer surface to selectively generate thesink in the stepped part having the outside air inlet part or slitformed thereon, and the generation of sink in the surface subjected totransfer can be more effectively prevented to mold a molded producthaving a more precise transfer surface.

The stepped part may be formed, for example, so as to have a pluralityof continuous steps as described in the fourth object.

In the above structure, since the stepped part is formed so as have aplurality of continuous steps, the sink can be more widely generated inthe non-transfer part to more effectively prevent the generation of sinkin the surface subjected to transfer, and a molded product having a moreprecise transfer surface can be molded.

Further, the stepped part is formed, for example, so as to have aplurality of continuous steps, and the outside air inlet part or slitmay be formed in the state communicating with the cavity in the areabetween the steps as described in the fifth object.

In this structure, since the stepped part is formed so as to have aplurality of continuous steps, and the outside air inlet part or slit isformed in the state communicating with the cavity in the area betweenthe steps, the sink can be more widely generated in the non-transferpart to more effectively prevent the generation of sink in the surfacesubjected to transfer, and a molded product having a more precisetransfer surface can be molded.

The above-mentioned resin molding device may farther comprise, forexample, a gas feeding means for forcedly feeding a prescribed gas tothe outside air inlet part or slit to feed the gas into the cavitythrough the outside air inlet part or slit by the gas feeding meansduring and after the injection of the molten resin into the cavity asdescribed in the sixth object.

In this structure, since the gas feeding means for forcedly feeding theprescribed gas to the outside air inlet part or slit is connected tofeed the gas into the cavity through the outside air inlet part or slitduring and after the injection of the molten resin into the cavity bythe gas feeding means, the timing of sink generation can be hastened tomore effectively prevent the generation of sink in the surface subjectedto transfer in the transfer of the surface of a part slightly distantfrom the sink position or the like, and the cooling can be rapidlyprogressed to mold a molded product having a more precise transfersurface.

Further, the above-mentioned resin molding device further may comprise,for example, a gas feeding means for forcedly feeding a prescribed gasto the outside air inlet part or slit to feed the gas into the cavitythrough the outside air inlet part or slit by the gas feeding meansafter the injection of the molten resin into the cavity as described inthe seventh object.

In this structure, since the gas feeding means for forcedly ceding theprescribed gas to the outside air inlet part or slit is connected tofeed the gas into the cavity through the outside air inlet part or slitafter the injection of the molten resin into the cavity by the gasfeeding means, the resin surface in the periphery of the outside airinlet part or slit can be separated from the metal mold surface whilesuppressing the entrainment of gas by the resin to guide the sink to anoptional position, the timing of sink generation can be hastened to moreeffectively prevent the generation of sink in the surface subjected totransfer in the transfer of the surface of a part slightly distant fromthe sink position or the like, and the cooling can be rapidly progressedto mold a mold product, even if relatively thin, having a more precisetransfer surface.

A resin molding method for molding a resin molded product by injecting amolten resin into the cavity of a metal mold followed by solidificationaccording to the eighth object comprises injecting the molten resin inthe state where it climbs over a stepped part formed within the cavityof the metal mold orthogonally to the flowing direction of the moltenresin introduced into the cavity while introducing the outside air intothe cavity through a prescribed outside air inlet part formed on themetal mold and opened to an optional part of the cavity to allow theoutside of the metal mold to communicate with the cavity inside.

In this structure, since the molten resin is injected in the state whereit climbs over the stepped part formed within the cavity of the metalmold orthogonally to the flowing direction of the molten resin injectedinto the cavity while introducing the outside air into the cavitythrough the prescribed outside air inlet part formed on the metal moldand opened to an optional part of the cavity to allow the outside of themetal mold to communicate with the cavity inside in the molding of theresin molded product by injecting the molten resin into the cavity ofthe metal mold followed by solidification, the sink can be selectivelygenerated in the resin of the outside air inlet part portion formed inan optional part except the transfer surface to prevent the generationof sink in the surface subjected to transfer in a low-pressure moldingcondition without using any special or expensive device, and a moldedproduct having a precise transfer surface can be molded at a low costwith low energy consumption.

A resin molding method for molding a resin molded product by injecting amolten resin into the cavity of a metal mold followed by solidificationaccording to the ninth object comprises injecting the molten resin inthe state where it climbs over a stepped part formed within the cavityof the metal mold orthogonally to the flowing direction of the moltenresin introduced into the cavity while introducing the outside air intothe cavity through a slit formed on the metal mold to allow an optionalpart of the cavity to communicate with the outside of the metal mold.

In this structure, since the molten resin is injected in the state whereit climbs over the stepped part formed within the cavity of the metalmold orthogonally to the flowing direction of the molten resin injectedinto the cavity while introducing the outside air into the cavitythrough the slit formed on the metal mold to allow the optional part ofthe cavity to communicate with the outside of the metal mold, the sinkcan be selectively generated in the resin of the slit part formed in anoptional part except the transfer surface to prevent the generation ofsink in the surface subjected to transfer in a low-pressure moldingcondition without using any special or expensive device, and a moldedproduct having a precise transfer surface can be molded at a lower costwith lower energy consumption by use of the cavity precisely formedwithout providing any limitation to the metal mold member.

The outside air inlet part or slit in the eighth and ninth objects maybe formed, or example, in the stepped part or the boundary of steps ofthe stepped part as described in the tenth object.

In this structure, since the outside air inlet part or slit is formed inthe stepped part or the boundary of steps of the stepped part, thestepped part and the outside air inlet part or slit can be formed in anoptional part except the transfer surface to selectively generate thesink in the stepped part having the outside air inlet part or slitformed thereon, and the generation of sink in the surface subjected totransfer can be more effectively prevented to mold a molded producthaving a more precise transfer surface.

The stepped part may be formed, for example, so as to have a pluralityof continuous steps as described in the eleventh object.

In this structure, since the stepped part is formed so as to have aplurality of continuous steps, the sink can be more widely generated inthe non-transfer part to more effectively prevent the generation of sinkin the surface subjected to transfer, and a molded product having a moreprecise transfer surface can be molded.

The stepped part may formed, for example, so as to have a plurality ofcontinuous steps, so that the outside air inlet part or slit can beformed in the state communicating with the cavity in the area betweenthe steps as described in the twelfth object.

In this structure, since the stepped part is formed so as to have aplurality of continuous steps, and the outside air inlet part or slit isformed in the state communicating with the cavity in the area betweenthe steps, the sink can be more widely generated in the non-transferpart to more effectively prevent the generation of sink in the surfacesubjected to transfer, and a molded product having a more precisetransfer surface can be molded.

A prescribed gas may be fed into the cavity through the outside airinlet part or slit by a gas feeding means for forcedly feeding the gasto the outside air inlet part or slit during and after the injection ofthe molten resin into the cavity, for example, as described in thethirteenth object.

In this structure, since the prescribed gas is fed into the cavitythrough the outside air inlet part or slit during and after theinjection of the molten resin into the cavity by the gas feeding meansfor forcedly feeding the gas to the outside air inlet part or slit, thetiming of sink generation can be hastened to more effectively preventthe generation of sink in the surface subjected to transfer in thetransfer of the surface of a part slightly distant from the sinkposition or the like, and the cooling can be rapidly progressed to molda molded product, even if relatively thin, having a more precisetransfer surface.

The prescribed gas may be fed into the cavity through the outside airinlet part or slit by the gas feeding means for forcedly feeding the gasto the outside air inlet part or slit after the injection of the moltenresin into the cavity, for example, as described in the fourteenthobject.

In this structure, since the prescribed gas is fed into the cavitythrough the outside air inlet part or slit after the injection of themolten resin into the cavity by the gas feeding means for forcedlyfeeding the gas to the outside air inlet part or slit, the resin surfacein the periphery of the outside air inlet part or slit can be separatedfrom the metal mold surface to guide the sink to an optional position,the timing of sink generation can be hastened to more effectivelyprevent the generation of sink in the surface subjected to transfer inthe transfer of the surface of a part slightly distant from the sinkposition or the like, and the cooling can be rapidly progressed to molda molded product, even if relatively thin, having a more precisetransfer surface.

A resin molded product according to the fifteenth object is molded byuse of a resin molding device described in any one of the first, second,fourth, sixth and seventh objects or according to a resin molding methoddescribed in any one of the eighth, ninth, eleventh, thirteenth andfourteenth objects, and comprises a non-transfer part formed in theoutside air inlet part or slit part.

In this structure, since the resin molded product is molded by use ofthe resin molding device described in any one of the first, second,fourth, sixth and seventh objects or according to the resin moldingmethod described in any one of the eighth, ninth, eleventh, thirteenthand fourteenth objects, and the non-transfer part is formed in theoutside air inlet part or slit part, the transfer property of thetransfer surface near the non-transfer part can be enhanced to provide aprecise transfer surface.

A resin molded product according to the sixteenth object is molded byuse of a resin molding device described in either of the third and fifthobjects or according to a resin molding method described in either ofthe tenth and twelfth objects, and comprises a non-transfer part formedin the stepped part or the boundary of steps of the stepped part.

In this structure, since the resin molded product is molded by the useof the resin molding device described in either of the third and fifthobjects or according to the resin molding method described in either ofthe tenth and twelfth objects, and the non-transfer part is formed inthe stepped part or the boundary of steps of the stepped part, thetransfer property of the transfer surface near the non-transfer part canbe enhanced to provide a precise transfer surface.

A resin molded product according to the seventeenth object is molded byuse of a resin molding device described in any one of the first toseventh objects or according to a resin molding method described in anyone of the eighth to fourteenth objects and by using a metal mold havinga tooth part recessed part for forming the tooth part of a gear withinthe cavity on the molten resin-flowing directional downstream side fromthe stepped part as the metal mold, and comprises the tooth part formedthereon.

In this structure, since the resin molded product is molded by the resinmolding device described in any one of the first to seventh objects oraccording to the resin molding method described in any one of the eighthto fourteenth objects and by use of the metal mold having the tooth partrecessed part for forming the tooth part of the gear within the cavityon the molten resin-flowing directional downstream side from the steppedpart as the metal mold, and comprises the tooth part formed thereon, thetransfer property of the tooth part that is an irregular-shaped powertransmission part can be enhanced to provide a precise gear shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan sectional view of a rein molding metal mold accordingto a first embodiment of the resin molding device, resin molding methodand resin molded product of this invention, which is taken along theline Y-Y of FIG. 2.

FIG. 2 is an enlarged front sectional view of the stepped part of theresin molding metal mold of FIG. 1, which is taken along the line X-X ofFIG. 1.

FIG. 3 is an enlarged front sectional view of the stepped part of theresin molding metal mold of FIG. 2 where a molten resin is beinginjected thereto.

FIG. 4 is an enlarged plan view of the stepped part of the resin moldingmetal mold of FIG. 2.

FIG. 5 is a perspective view of the stepped part of the resin moldingmetal mold of FIG. 2.

FIG. 6 is an enlarged front sectional view of the stepped part of FIG. 2dimensionally showing the steps and thickness thereof.

FIG. 7 is an enlarged front sectional view of the stepped part of FIG. 2dimensionally showing the steps and thickness thereof when the moltenresin is being injected to the stepped part.

FIG. 8 is a perspective view of the stepped part of the resin moldingmetal mold of FIG. 5 when the resin is injected in parallel thereto.

FIG. 9 is a partially enlarged front sectional view of the resin moldingmetal mold of FIG. 1 in the state where a gas-feeding machine isconnected to the outside air inlet part.

FIG. 10 is a partially enlarged front sectional view of the resinmolding metal mold of FIG. 9 in the state filled with the resin.

FIG. 11 is a plan sectional view of a resin molding metal mold accordingto a second embodiment of the resin molding device, resin molding methodand resin molded product of this invention.

FIG. 12 is an enlarged front sectional view of the stepped part of theresin molding metal mold of FIG. 11.

FIG. 13 is an enlarged front sectional view of the stepped part of theresin molding metal mold of FIG. 12 when the molten resin is beinginjected thereto.

FIG. 14 is an enlarged front sectional view of the stepped part of theresin molding metal mold of FIG. 13 showing the state where the moltenresin injected thereto causes a sink in the slit part.

FIG. 15 is a perspective view of the stepped part of the resin moldingmetal mold of FIG. 13.

FIG. 16 is a plan sectional view of a resin molding metal mold accordingto a third embodiment of the resin molding device, resin molding methodand resin molded product of this invention.

FIG. 17 is an enlarged front sectional view of the stepped part of theresin molding metal mold of FIG. 16.

FIG. 18 is an enlarged front sectional view of the stepped part of theresin molding metal mold of FIG. 17 where the molten resin is beinginjected thereto.

FIG. 19 is a plan view of the stepped part of the resin molding metalmold of FIG. 17.

FIG. 20 is an enlarged front sectional view of the stepped part of FIG.17 dimensionally showing the steps and thickness thereof.

FIG. 21 is an enlarged front sectional view of the stepped part of FIG.17 dimensionally showing the steps and thickness thereof when the moltenresin is being injected to the stepped part.

FIG. 22 is a front sectional view of the resin molding metal mold ofFIG. 16.

FIG. 23 is a front sectional view of the resin molding metal mold ofFIG. 22 in the state where the molten resin is being injected up to thestepped portion thereof.

FIG. 24 is a front sectional view of the resin molding metal mold ofFIG. 22 showing the state where the cavity is filled with the moltenresin, and a sink is generated.

FIG. 25 is a front view of a molded product formed by use of aconventional resin molding metal mold where a sink is generated in thetransfer part.

FIG. 26 is a front view of a molded product formed by use of the resinmolding metal mold of FIG. 16 where a sink is generated in the transferpart.

FIG. 27 is an enlarged front sectional view of the stepped part of theresin molding metal mold where the cavity is changed from a largeopening diameter state to a small opening diameter state.

FIG. 28 is an enlarged front sectional view of the stepped part of theresin molding metal mold of FIG. 27 in the state where the molten resinis injected thereto.

FIG. 29 is a partially enlarged front sectional view of the resinmolding metal mold of FIG. 16 in the state where a gas feeding machineis connected to the slit.

FIG. 30 is a partially enlarged frontsectional view of the resin moldingmetal mold of FIG. 29 in the state filled with the resin.

FIG. 31 is a front sectional view of a resin molding metal moldaccording to a fourth embodiment of the resin molding device, resinmolding method and resin molded product of this invention.

FIG. 32 is a front view of a molded product formed by use of the resinmolding metal mold of FIG. 31.

FIG. 33 is a plan sectional view of a resin molding metal mold accordingto a fifth embodiment of the resin molding device, resin molding methodand resin molded product of this invention.

FIG. 34 is a front sectional view of the resin molding metal mold ofFIG. 33.

FIG. 35 is a front view of a gear as the molded product formed by use ofthe resin molding metal mold of FIG. 33.

FIG. 36 is a front sectional view of the resin molding metal mold ofFIG. 33 where the stepped part of the resin molding metal mold has aplurality of steps.

FIG. 37 is a front view of a gear as the molded product formed by use ofthe resin molding metal mold of FIG. 36.

FIG. 38 is a plan sectional view of a resin molding metal mold accordingto a sixth embodiment of the resin molding device, resin molding methodand resin molded product of this invention.

FIG. 39 is an enlarged front sectional view of the stepped part of theresin molding metal mold of FIG. 38.

FIG. 40 is a front view of a molded product formed by use of the resinmolding metal mold of FIG. 38.

FIG. 41 is a front sectional view of a resin molding metal moldaccording to a seventh embodiment of the resin molding device, resinmolding method and resin molded product of this invention.

FIG. 42 is an enlarged front sectional view of the stepped part of theresin molding metal mold of FIG. 41.

FIG. 43 is a front view of a molded product formed by use of the resinmolding metal mold of FIG. 41.

FIG. 44 is an enlarged front view of a non-transfer part in a resinmolded product formed by use of a resin molding metal mold having aone-step stepped part.

FIG. 45 is an enlarged front view of another example of the non-transferpart in the resin molded product formed by use of the resin moldingmetal mold having the one-step stepped part.

FIG. 46 is an enlarged front view of a non-transfer part in a resinmolded product formed by use of a resin molding metal mold having astepped part having a plurality of tapered steps.

FIG. 47 is an enlarged front view of another example of the non-transferpart in the resin molded product formed by use of the resin moldingmetal mold having the stepped part having a plurality of tapered steps.

FIG. 48 is an enlarged front sectional view of a slit part of a resinmolding metal mold having only a slit without having any stepped part.

FIG. 49 is an enlarged front sectional view of the slit part of theresin molding metal mold of FIG. 48 in the state where the molten resinflows into the slit part to form a sink.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of this invention are further described in detailon the basis of accompanying drawings. Various technically preferablelimitations are given to the following embodiments because of thepreferred embodiments of this invention. However, the scope of thisinvention is never limited to these embodiments unless the limitation ofthis invention is particularly described in the following descriptions.

FIGS. 1-8 show a first embodiment of the resin molding device, resinmolding method and resin molded product of this invention, and FIG. 1 isa plan sectional view of a resin molding metal mold 1 according to thefirst embodiment of the resin molding device, resin molding method andresin molded product of this invention.

In FIG. 1, the resin molding metal mold 1 that is a resin molding devicehas a plurality of gates 3 opened to a cavity 2 in the central part, andthe cavity 2 is formed in a hollow disc shape. In the resin moldingmetal mold 1, a molten resin 10 introduced into the cavity 2 from thegates 3 (refer to FIGS. 2 and 3) spreads and flows radially from thehollow substantially disc-shaped central part as shown by arrows in FIG.1 to fill the cavity 2.

As the molten resin 10 as the molding material, a resin such ascrystalline resin, amorphous resin, elastomer or the like having thecontracting property in the solidification of the material can be used,and a resin material containing, for example, inorganic filler, metalpowder, magnetic powder or the like is also usable.

A stepped part 4 is circularly formed within the cavity 2, as shown inFIGS. 1-5, orthogonally to the flowing direction of the molten resin 10introduced into the cavity 2 from the gates 3 or circumferentially, anda fine outside air inlet part 5 is circularly formed on the outer sideof the stepped part 4, as shown in FIGS. 1-4, orthogonally to theflowing direction of the molten resin 10 or circumferentially. Theoutside air inlet part 5 is allowed to communicate with the outside airthrough a communicating passage 6 opened to the outside of the resinmolding metal mold 1 as shown in FIGS. 2 and 3. The outside air inletpart 5 and the communicating passage 6 function as an outside air inletpart as the whole.

The cavity 2 is formed so that the opening diameter is larger in theouter side of the stepped part 4 as shown in FIGS. 2 and 3, and thestepped part 4 is formed as large as possible within a range allowablein the whole design of a resin molded product with a step S of 20 μm ormore as shown in FIGS. 6 and 7. The step S is desirably set to S≧t/10 tothe thickness t of the molded product.

The outside air inlet part 5 is formed of a porous member, at least onefine slit (clearance), or a movable member, and formed in the directionwhere the molten resin 10 crosses over the outside air inlet part 6during flowing in the cavity 2, or in the circumferential directionwhere the molten resin 10 flowing radially from the central part of thecavity 2 crosses over it.

The effect of this embodiment is described. In the resin molding metalmold 1, the molten resin 10, when infected from the gates 3 formed inthe central part of the cavity 2, flows radially from the central partof the cavity 2 as shown by the arrows in FIG. 1, and successivelypasses the circumferentially formed stepped part 4 and outside air inletpart 6 to fill the outermost part of the cavity 2.

The cavity 2 is formed so that the opening diameter is increased withthe stepped part 4 as the boundary as shown in FIGS. 2, 3, 6 and 7 tochange the molded product shape from a thin part to a thick part. Whenthe molten resin 10 flows from the thin part to the thick part, itspressure is released due to the presence of the stepped part 4 withinthe cavity 2 to weaken the force of pressing the molten resin 10 to thewall surface of the resin molding metal mold 1. Accordingly, anon-transfer part is apt to be formed in the edge part of the steppedpart 4 because the molten resin 10 is not sufficiently intruded thereto.This non-transfer part is apt to start to induce a sink in coolingprocess because its adhesive force to the resin molding metal mold 1 issmaller than that of the other part. It is particularly effective to setthe step S of the stepped part 4 to s≧t/10 to the thickness t of themolded product.

It is important to form the stepped part 4 orthogonally to the flowingdirection of the molten resin 10 as shown in FIGS. 1-7. When it isformed in the direction parallel to the flowing direction (the arroweddirection in FIG. 8) of the molten resin as shown in FIG. 8, the moltenresin 10 gets into the edge part of the stepped part 4, and the aboveeffect cannot be provided.

Since the surface layer of the molten resin 10 is closely fitted to theresin molding metal mold 1 in the flowing process, the heat of themolten resin 10 is instantaneously drained by the resin molding metalmold 1 to solidify it. This phenomenon is particularly remarkable when aresin passage or the cavity 2 has a thin or narrow shape, and thisflowing manner of the molten resin 10 is called a fountain flow. Whenthe cavity 2 has a thick shape, to the contrary, the molten resin 10flows not necessarily closely fitting to the resin molding metal mold 1,and this flowing manner is different from the fountain flow as jettingphenomenon.

In the resin molding metal mold 1 of this embodiment, the fine outsideair inlet part 5 allowed to communicate with the outside through thecommunicating passage 6 is formed in the thick part orthogonally to theflowing direction of the molten resin 10, and the flowing molten resin10 generates a sink to the thick part by the outside air introduced fromthe outside air inlet part 5.

When the filing of the cavity 2 with the molten resin 10 is completed,the gates 3 are sealed to perform a pressure retaining process. In thepressure retaining process, also, the part facing the outside air inletpart 5 of the resin 10 is in contact with the outside air to progressthe sink. Namely, even in the pressure retaining process up to thesealing of the gates 3 by the cooling and solidification of the resin inthe gate part after the completion of the filling with the molten resin10, the part facing the outside air inlet part 5 of the resin 10 is incontact with the outside air to keep the state more easily generable ofsink than the other part.

The cooling process is performed after the completion of the pressureretaining process. In this cooling process, the resin 10 is generallycontracted in volume. The resin 10 of the surface part continuouslykeeps the close fitting with the resin molding metal mold 1 while thepressure of the resin 10 in the resin molding metal mold 1 is not zero.However, when the resin pressure in the resin molding metal mold 1lowers according to cooling and gets close to zero, the central part ofthe thick part is cooled, solidified and contracted last. Accordingly,the resin 10 around the central part of the thick part is pulled towardthe central part of the thick part. Since the surface layer part of theresin 10 having the weakest dose fitting force to the resin moldingmetal mold 1 is easily released from the resin molding metal mold 1, theresin 10 starts to move toward the central part of the thick part,consequently forming a recessed non-transfer part called sink In theresin molding metal mold 1 of this embodiment, however, since theoutside air inlet part 5 is formed in the thick part and in contact withthe outside air, only the part facing the outside air inlet part 5 islaid in the state where the close fitting force to the resin moldingmetal mold 1 is released, and the part facing the outside air inlet part5, where the close fitting force to the resin molding metal mold 1 isweak, is easily pulled toward the thick central part and moved.

Accordingly, the sink can be selectively generated in the resin 10 partfacing the outside air inlet part 5 or a molded product part to form thenon-transfer part.

When the sink is once generated, this part is relatively higher intemperature than the part making contact with the resin molding metalmold 1 because the cooling from the resin molding metal mold 1 isarrested, and more easily moved because of the low viscosity of theresin 10 to progress the sink.

This sink is progressed, whereby the part subjected to transfer can beless pulled to the thick part by this portion to prevent the sink orcontracting deformation of the transfer part.

The outside air inlet part 5 is formed on the resin molding metal mold 1of the position forming the non-transfer part of the molded product,whereby the non-transfer part can be formed in the part facing theoutside air inlet part 5 to improve the transfer property of thetransfer part, so that the shape precision of the molded product can beimproved, and transfer of surface state such as wrinkle, transfer offine surface shape or the like can be easily and precisely performed.

It is more effective to enlarge the sink in the non-transfer part of thepart facing the outside air inlet part 5. However, when the pressure ofthe molten resin 10 is too high in the injection filling process offilling the molten resin 10 and the pressure retaining process, themolten resin 10 is cooled and solidified before the internal pressure ofthe molten resin 10 becomes zero, so that the sink is hardly generated,and the generation effect of sink in the non-transfer part of the partfacing the outside air inlet part 5 can not be properly provided.Accordingly, it is important to perform a low-pressure molding in theinjection filling process and the pressure retaining process.

When the low-pressure molding is performed, the residual stress to themolded product can be reduced, and a molded product excellent in agingstability can be molded.

In this embodiment, a gas feeding machine (gas feeding means) 7 such aspump may be connected to the communicating passage 6, as shown in FIG.9, to introduce a prescribed gas such as air to the cavity 2 through thecommunicating passage 6 and the outside air inlet part 5. The gasintroduced by the gas ceding machine 7 may have a low pressure of about1-6 kgf/cm2.

The gas feeding machine 7 may be driven during and after the filling ofthe molten resin 10 into the cavity 2 to introduce the gas into thecavity 2 through the communicating passage 6 and the outside air inletpart 5, or driven only after the fling of the molten resin 10 into thecavity 2 to introduce the gas into the cavity 2 through thecommunicating passage 6 and the outside air inlet part 5.

Accordingly to this, the resin 10 of the part acing the outside airinlet part 5 can be more efficiently cooled to hasten the timing of sinkgeneration, and the sink of the resin 10 of this part can be enlargedmore to improve the transfer property of the transfer surface furthermore. When the gas feeding machine 7 is driven during the filling tointroduce the gas into the cavity 2, particularly, the resin 10 of thepart acing the outside air inlet part 5 can be made hardly fitted to themetal mold surface of the resin molding metal mold 1. Accordingly, evenin the cooling process, the resin of this part is easily released fromthe metal mold surface to facilitate the formation of the sink. Thetransfer property of the transfer surface can be improved further moreby enlarging the sink of this part more.

In this embodiment, a recessed part 8 for forming a protrudingprojection or rib on the molded product may be further formed on thecavity 2 surface of the resin molding metal mold 1 between the outsideair inlet part 5 and a transfer surface 9 as shown in FIG. 10. The gasfeeding machine 7 is connected to the communicating passage 6communicating with the outside air inlet part 5, and the gas feedingmachine 7 is driven after and during the filling of the molten resin 10into the cavity 2 or after the filling to introduce the gas into thecavity 2 through the communicating passage 6 and the outside air inletpart 5.

Accordingly to this, even if the transfer surface 9 is located in aposition close to the sink generating position of the resin 10 fadingthe outside air inlet part 5, the generated surface sink area cannotspread over the rib since the resin in the protruding rib part of themolded product is rapidly cooled and solidified. Accordingly, thesurface sink, generated relatively near the transfer surface 9 can beprevented from extending to the transfer surface and deteriorating theprecision of the transfer surface 9 to improve the transfer property ofthe transfer surface 9 flyer more.

In FIG. 10, the same gas feeding machine 7 as in FIG. 9 is connected tothe communicating passage 6 communicating with the outside air inletpart 5, but the same effect can be obtained without the gas feedingmachine 7. When the gas feeding machine 7 is provided, the resin 10 ofthe part facing the outside air inlet part 5 can be more efficientlycooled to hasten the timing of sink generation, and the sink of theresin 10 of this part can be more enlarged to improve the transferproperty of the transfer surface 9 further more. When the air feedingmachine 7 is driven after the filling of the resin, particularly, theresin 10 starts to sink at the timing that the resin pressure is lowerthan the gas introducing pressure before the internal pressure of theresin 10 of the part facing the outside air inlet part 5 is zero.Accordingly, the sink of the resin 10 of this part can be enlarged moreto improve the transfer property of the transfer surface 9 further more.

FIGS. 11-15 show a second embodiment of the resin molding device, resinmolding method and resin molded product of this invention, and FIG. 11is a plan view of a resin molding metal mold 20 according to the secondembodiment of the resin molding device, resin molding method and resinmolded product of this invention.

This embodiment is applied to the same resin molding metal mold as theresin molding metal mold 1 of the first embodiment, and the samereference number is imparted to the same component as in the firstembodiment to omit the detailed description therefor.

In FIG. 11, the resin molding metal mold 20 that is a resin moldingdevice has a plurality of gates 3 opened to a cavity 2 in the centralpart, and the cavity 2 is formed in a hollow disc shape. In the resinmolding metal mold 20, a molten resin 10 introduced into the cavity 2through the gates 3 spreads and flows radially from the central part ofthe cavity 2 as shown by arrows in FIG. 11 to fill the cavity 2.

A stepped part 4 is circularly formed within the cavity 2, as shown inFIGS. 11-15, orthogonally to the flowing direction of the molten resin10 introduced into the cavity 2 from the gate 3 or circumferentially,and a fine slit 21 is circularly formed on the outer side of the steppedpart 4, as shown in FIGS. 11-14, orthogonally to the flowing directionof the molten resin 10 or circumferentially. The slit 21 is allowed tocommunicate with the outside air out of the resin molding metal mold 20.

The slit 21 is formed in a width L of about 1-30 μm in the directionwhere the molten resin 10 crosses over the slit 21 during flowing in thecavity 2 or in the circumferential direction where the molten resin 10flowing radially from the central part of the cavity 2 crosses over it.

The effect of this embodiment is described. In the resin molding metalmold 20 of this embodiment, the molten resin 10, when injected from thegates 3 formed in the central part of the cavity 2, flows radially fromthe central part of the cavity 2 as shown. by the arrows in FIG. 11, andsuccessively passes the circumferentially formed stepped part 4 and slit21 to fill the outermost part direction of the cavity 2.

The cavity 2 is formed so that the opening diameter is increased withthe stepped part 4 as the boundary as shown in FIGS. 12-15 to change themolded product shape from a thin part to a thick part. When the moltenresin 10 flows from the thin part to the thick part, its pressure isreleased due to the presence of the stepped part 4 within the cavity 2to weaken the force of pressing the molten resin 10 to the wall surfaceof the resin molding metal mold 20. Accordingly, a non-transfer part isapt to be formed in the edge part of the stepped part 4 because themolten resin 10 is not sufficiently intruded thereto. The non-transferpart is apt to start to induce a sink in cooling process because itsadhesive force to the resin molding metal mold 20 is smaller than thatof the other part. It is particularly effective to set the step S of thestepped part 4 to s≧t/10 to the thickness t of the molded product.

Since the surface layer of the molten resin 10 is closely fitted to theresin molding metal mold 20 in the flowing process, the heat of themolten resin 10 is instantaneously drained by the resin molding metalmold 20 to solidify it.

The resin molding metal mold 20 has the slit 21 formed in the thick partorthogonally to the flowing direction of the molten resin 10. Therefore,the molten resin 10 flowing while closely fitting to the inner surfaceof the resin molding metal mold 20 by the fountain flow cannot get intothe fine slit 21 when it flows on the slit 21, and moves in contact withthe outside air introduced from the slit 21 to generate a sink in thethick part by the outside air introduced from the slit 21.

Namely, even in the pressure retaining process up to the sealing of thegates 3 by the cooling and solidification of the resin 10 in the gatepart after the completion of the filling of the molten resin 10 into thecavity 2, the part facing the slit 21 of the resin 10 is in contact withthe outside air as shown in FIG. 24 to keep the state more easilygenerable of sink than the other part.

The cooling process is performed after the completion of the pressureretaining process. In this cooling process, the resin 10 is generallycontracted in volume. The resin 10 of the surface part continuouslykeeps the close fitting with the resin molding metal mold 20 while thepressure of the resin 10 in the resin molding metal mold 20 is not zero.However, when the resin pressure in the resin molding metal mold 20lowers according to cooling and gets close to zero, the central part ofthe thick part is cooled, solidified and contracted last as shown inFIG. 14. Accordingly, the resin 10 around the central part of the thickpart is pulled toward the central part of the thick part. Since thesurface layer part of the resin 10 having the weakest close fittingforce to the resin molding metal mold 20 is easily separated from theresin molding metal mold 20, the resin 10 starts to move toward thecentral part of the thick part, consequently forming a recessednon-transfer part called sink.

In this resin molding metal mold 20 of this embodiment, however, sincethe slit 21 is formed in the thick part and in contact with the outsideair, only the part facing the slit 21 is laid in the state where theclose fitting force to the resin molding metal mold 20 is released, andthe part facing the slit 21, where the close fitting force to the resinmolding metal mold 20 is weak, is easily pulled toward the thick centralpart and moved.

Accordingly, the sink can be selectively generated in the resin 10 partfacing the slit 21, as shown in FIG. 14, or the molded product part toform the non-transfer part.

When the sink is once generated, this part is relatively higher intemperature than the part making contact with the resin molding metalmold 20 since the cooling from the resin molding metal mold 20 isarrested, and easily moved because of the low viscosity of the resin 10to progress the sink.

This sink is progressed, whereby the part subjected to transfer can beless pulled to the thick part by this portion to prevent the sink orcontracting deformation of the transfer part.

Accordingly, the slit 21 is formed in the resin molding metal mold 20 ofthe position forming the non-transfer part of the molded product,whereby the non-transfer part can be formed in the part facing the slit21 to improve the transfer property of the transfer part, so that theshape precision of the molded product can be improved, and transfer ofsurface state such as wrinkle, transfer of fine surface shape or thelike can be easily and precisely performed.

It is more effective to enlarge the sink in the non-transfer part of thepart facing the slit 21. However, when the pressure of the resin 10 istoo high in the injection filling process of filling the molten resin 10and the pressure retaining process, the resin 10 is cooled andsolidified before the internal pressure of the resin 10 becomes zero,the sink is hardly generated, and the generation effect of sink in thenon-transfer part of the part facing the slit 21 cannot be properlyprovided. In this embodiment, also, it is important to perform alow-pressure molding in the injection filling process and the pressureretaining process.

When the low-pressure molding is performed, the residual stress to themolded product can be reduced, and a molded product excellent in agingstability can be molded.

FIGS. 16-26 show a third embodiment of the resin molding device, resinmolding method and resin molded product of this invention, and FIG. 16is a plan view of a resin molding metal mold 30 for molding a resinmolded product according to the third embodiment of the resin moldingdevice, resin molding method and resin molded product of this invention.

This embodiment is applied to the same resin molding metal mold as theresin molding metal mold 1 of the first embodiment, and the samereference number is imparted to the same component as in the firstembodiment to omit the detailed description therefor.

In FIG. 16, the resin molding metal mold 30 that is a resin moldingdevice has a plurality of gates 3 opened to a cavity 2 in the centralpart, and a molten resin 10 introduced into the cavity 2 from the gates3 radially extends and flows to fill the cavity 2 as shown by arrows inFIG. 16.

A stepped part 31 is circularly formed within the cavity 2 as shown inFIGS. 16-21 orthogonally to the flowing direction of the molten resin 10introduced into the cavity 2 from the gates 3 or circumferentially, anda slit 32 is formed in the part of the stepped part 31. The slit 32 isformed on the thick part side of the stopped part 31 and allowed tocommunicate with the outside air in the outside of the resin moldingmetal mold 30.

The cavity 2 is formed so that the opening diameter is larger in theouter side of the stepped part 4 as shown in FIGS. 17, 18, 20 and 21,and the stepped part 4 is formed as large as possible within a rangeallowable in the whole design of a molded product with a step S of 20 μmor more as shown in FIGS. 20 and 21. It is particularly desirable to setthe step S to s≧t/10 to the thickness t of the molded product.

The slit 32 is formed in a width L of about 1-30 μm in the directionwhere the molten resin 10 crosses over the slit 32 during flowing in thecavity 2 or the circumferential direction where the molten resin 10flowing radially from the central part of the cavity 2 crosses over it.

The effect of this embodiment is described. In the resin molding metalmold 30 of this embodiment, as shown in FIG. 23, the molten resin 10,when injected to the central part of the cavity 2 from the gates 3,flows radially from the central part of the cavity 2 as shown in FIGS.16 and 22, and successively passes the circumferentially formed steppedpart 31 and slit 32 to fill the outermost part direction of the cavity2.

The cavity 2 is formed so that the opening diameter is increased withthe stepped part 31 as the boundary as shown in FIGS. 16-18 and 20-24 tochange the molded product shape from a thin part to a thick part. Whenthe molten resin 10 flows from the thin part to the thick part, itspressure is released due to the presence of the stepped part 31 withinthe cavity 2 to weaken the force of pressing the molten resin 10 to thewall surface of the resin molding metal mold 30. Accordingly, anon-transfer part is apt to be formed in the edge part of the steppedpart 31 because the molten resin 10 is not sufficiently intrudedthereto. The non-transfer part is apt to start to induce a sink in thecooling process since its adhesive force to the resin molding metal mold30 is smaller than that of the other part. It is particularly effectiveto set the step S of the stepped part 31 to s≧t/10 to the thickness t ofthe molded product.

Since the slit 32 is formed in the stepped part 31, the molten resin 10flowing while closely fitting to the inner surface of the resin moldingmetal mold 30 by the fountain flow does not get into the edge parthaving the slit 32 formed thereon as described above in the stepped part31, and cannot intrude into the fine slit 32 when it flows on the slit32. Accordingly, the molten resin 10 moves in contact with the outsideair introduced from the slit 32 to cause a sink in the part acing thestepped part 31 by the outside air introduced from the slit 32.

Namely, even in the pressure retaining process up to the sealing of thegates 3 by the cooling and solidification of the resin 10 of the gatepart after the completion of the filling of the molten resin 10 into thecavity 2, the part facing the slit 32 of the resin 10 is still incontact with the outside air as shown in FIG. 24 to keep the state moreeasily generable of sink than the other part. At this time, a moltenresin 10 a, among the molten resin 10, in the central part of the cavity2 shown by an elliptic shape in FIG. 24 is laid in a state higher intemperature than the circumference.

The cooling process is performed after the completion of the pressureretaining process. In this cooling process, the resin 10 is generallycontracted in volume. The resin 10 of the surface part continuouslykeeps the close fitting with the resin molding metal mold 30 while thepressure of the resin 10 within the resin molding metal mold 30 is notzero. However, when the resin pressure within the resin molding metalmold 30 lowers according to cooling and gets close to zero, the centralpart 10 a of the thick part is cooled, solidified and contracted last asshown in FIG. 24. The resin 10 around the central part 10 a of the thickpart is thus pulled toward the central part 10 a of the thick part asshown by an arrow in FIG. 24.

Since the surface layer part of the resin 10 having the weakest closefitting force to the resin molding metal mold 30 is easily separatedfrom the resin molding metal mold 30, the resin 10 starts to move towardthe central part of the thick part in the past to form a recessednon-transfer part 101 called sink in a molded product 100 as shown inFIG. 25.

In the resin molding metal mold 30 of this embodiment, however, sincethe slit 32 is formed in the stepped part 31 and in contact with theoutside air, only the part facing the slit 32 of the stepped part 31 islaid in the state where the close fitting force to the resin moldingmetal mold 30 is released, and the part facing the slit 32, where theclose fitting force to the resin molding metal mold 30 is weak, iseasily pulled toward the thick central part and moved.

Accordingly the sink can be selectively generated in the resin 10 partfacing the slit 32 or the non-transfer part.

When the sink is generated once, this part is relatively high intemperature than the part making contact with the resin molding metalmold 30 because the cooling from the resin molding metal mold 30 isarrested, and more easily moved because of the low viscosity of theresin 10 to progress the sink.

This sink is progressed, whereby the part subjected to transfer can beless pulled to the thick part by this portion to prevent the sink orcontracting deformation of the transfer part.

The slit 32 is formed in the resin molding metal mold 30 of the positionforming a non-transfer part 111 of a molded product 110 as shown in FIG.26, whereby the non-transfer part 111 can be formed in the part lacingthe slit 32 to improve the transfer property of a transfer part 112, sothat the shape precision of the molded product 110 can be improved, andtransfer of surface state such as wrinkle, transfer of fine surfaceshape or the like can be easily and precisely performed.

It is more effective to enlarge the sink in the non-transfer part of thepart facing the slit 32. However, when the pressure of the molten resin10 is too high in the injection filling process of filling the moltenresin 10 and the pressure retaining process, the resin 10 is cooled andsolidified before the internal pressure of the resin 10 becomes zero,the sink is hardly generated, and the generation effect of sink in thenon-transfer part 111 of the part facing the slit 32 cannot be properlyprovided. Accordingly, it is important to perform a low-pressure moldingin the injection filling process and the pressure retaining process.

When the low-pressure molding is performed, the residual stress to themolded product can be reduced, and a molded product excellent in agingstability can be molded.

In this embodiment, the cavity 2 is changed from a small openingdiameter state to a large state in the stepped part 31 so as to changethe molded product shape from a thin part to a thick part. The steppedpart 33 may be formed so that the cavity 2 is changed from the largeopening state to the small state, as shown in FIGS. 27 and 28, and aslit 34 may be formed in the stepped part 33. In this case, also, thesame effect as the above embodiment can be provided.

In this embodiment, a gas feeding machine 35 such as pump may beconnected to the slit 32 as shown in FIG. 29 to introduce a prescribedgas such as air into the cavity 2 through the slit 32. In this case, thegas to be introduced by the gas feeding machine 35 may have a lowpressure of about 1-6 kgf/cm2.

The gas feeding machine 35 is driven during and after the filling of themolten resin 10 into the cavity 2 or only after the filling to introducethe gas into the cavity 2 through the slit 32.

According to this, the resin 10 of the part facing the slit 32 can bemore efficiently cooled to hasten the timing of sink generation, and thesink of the resin 10 of this part can be enlarged more to improve thetransfer property of the transfer surface further more. When the gasfeeding machine 35 is driven after the filling of the resinparticularly, the resin 10 starts to sink at the timing when the resinpressure becomes lower than the gas introducing pressure before theinternal pressure of the resin 10 of the part facing the slit 32 becomeszero, the sink of the resin 10 of this part can be enlarged more toimprove the transfer property of the transfer surface further more.

In this embodiment, as shown in FIG. 30, a recessed part 37 for forminga protruding projection or rib on the molded product may be furtherformed on the cavity 2 surface of the resin molding metal mold 30between the slit 32 and a transfer surface 36. The gas feeding machine35 is connected to the slit 32, and driven during and after the fillingof the resin 10 into the cavity 2 or only after the filling to introducethe gas into the cavity 2 through the slit 32.

According to this, the generated surface sink area cannot spread overthe rib even if the transfer surface 36 is present in a position closerto the sink generating position of the resin 10 acing the slit 32because the resin in the molded product protruding rib part is rapidlycooled and solidified. Accordingly, the surface sink generatedrelatively near the transfer surface 36 can be prevented from extendingto the transfer surface and deteriorating the precision of the transfersurface 36 to improve the transfer property of the transfer surface 36further more.

In FIG. 30, the same gas feeding machine 35 as in FIG. 29 is connectedto the slit 32, but the same effect can be obtained without the gasfeeding machine 35. When the gas feeding machine 35 is provided, thegenerated surface sink area cannot spread over the rib even if thetransfer surface 36 is present in a position close to the sinkgenerating position of the resin 10 facing the slit 32 because the resinof the molded product protruding rib part is rapidly cooled andsolidified. Accordingly, the surface sink generated relatively near thetransfer surface 36 can be prevented from extending to the transfersurface 36 and deteriorating the precision of the transfer surface 36 toimprove the transfer property of the transfer surface 36 further more.

FIGS. 31 and 32 show a fourth embodiment of the resin molding device,resin molding method and resin molded product of this invention, andFIG. 31 is a front sectional view of a resin molding metal mold 40 formolding a resin molded product according to the fourth embodiment of theresin molding device, resin molding method and resin molded product ofthis invention.

This embodiment is applied to the same resin molding metal mold as theresin molding metal mold 1 of the first embodiment, and the samereference number is imparted to the same component as in the firstembodiment to omit the detail description therefor.

In FIG. 31, the resin molding metal mold 40 that is a resin moldingdevice has a rib part 41 formed in the lower part of a flat plate-shapedcavity 2 and a plurality of gates 3 formed in the central part of thelower surface of the rib part 41, and a molten resin 10 introduced intothe cavity 2 from the gates 3 through the rib part 41 spreads and flowsradially from the rib part 41 in the central part of the cavity 2 tofill the cavity 2.

A stepped part 42 is formed in the vicinity of the cavity 2 of the ribpart 41 in the circumferential direction of the rib part 41, and a slit43 is formed in the portion of the stepped part 42. The slit 43 iscircumferentially formed on the thick part side of the stepped part 42and allowed to communicate with the outside The effect of thisembodiment is described. In the resin molding metal mold 40 of thisembodiment, as shown in FIG. 31, the molten resin 10, when injected fromthe gates 3 formed on the lower surface central part of the rib part 41,rises in the rib part 41 and successively passes the stepped part 42 andslit 32 formed in the circumferential direction of the rib part 41 tofill the cavity 2.

The rib part 41 is formed so that the opening diameter is larger withthe stepped part 42 as the boundary to change the molded product shapefrom a thin part to a thick part. When the molten resin 10 flows fromthe thin part to the thick part, its pressure is released due to thepresence of the stepped part 42 in the rib part 41 of the cavity 2 toweaken the force of pressing the molten resin 10 to the wall surface ofthe resin molding metal mold 40. A non-transfer part is thus apt to beformed in the edge part of the stepped part 42 because the molten resin10 is not sufficiently intruded thereto. The non-transfer part is apt tostart to induce a sink in the cooling process since its adhesive forceto the resin molding metal mold 40 is smaller than that of the otherpart.

Since the slit 43 is formed in the stepped part 42, the molten resin 10flowing while closely fitting to the inner surface of the resin moldingmetal mold 40 by the fountain flow does not get into the edge parthaving the slit 43 formed thereon as described above in the stepped part42, and cannot intrude into the fine slit 43 when it flows on the slit43. Accordingly, the molten resin 10 is moved in contact with theoutside air introduced from the slit 43 to generate a sink in the partacing the stepped part 42 by the outside air introduced from the slit43.

Accordingly, the sink can be selectively generated in the resin 10 partfacing the slit 43. When the sink is once generated, this part isrelatively higher in temperature than the part making contact with theresin molding metal mold 40 because the cooling from the resin moldingmetal mold 40 is arrested, and also more easily moved because of the lowviscosity of the resin 10 to progress the sink.

This sink is progressed, whereby the part subjected to transfer is lesspulled to the thick part by this portion to prevent the sink orcontracting deformation of the transfer part.

Accordingly, the slit 43 is formed in the resin molding metal mold 40 ofthe position forming a non-transfer part 121 of a molded product 120 asshown in FIG. 32, whereby the non-transfer part 121 is formed in thepart facing the slit 43 to improve the transfer property of a transferpart 122, so that the shape precision of the molded product 120 can beimproved, and transfer of surface state such as wrinkle, transfer offine surface shape or the like can be easily and precisely performed.

FIGS. 33-35 show a fifth embodiment of the resin molding device, resinmolding method and resin molded product of this invention, and FIG. 33is a plan view of a resin molding metal mold 50 for molding a resinmolded product according to the fifth embodiment of the resin moldingdevice, resin molding method and resin molded product of this invention,and FIG. 34 is a font sectional view of the resin molding metal mold 50.

In FIGS. 33 and 34, the resin molding metal mold 50 comprises a cavity51 having the shape of a gear 130 (refer to FIG. 35) as molded productin the inner part, and the cavity 51 comprises a major diameter part 51a for forming a gear part 132 having the tooth part 131 of the gear 130formed thereon, a minor diameter part 51 b for forming a shaft part 133of the gear 130, and a tooth part forming part 51 c for forming thetooth part 131 of the gear 130 protrusively formed on the outercircumferential surface of the major diameter part 51 a.

The resin molding metal mold 50 further comprises a gate 52communicating with the minor diameter part 51 b of the cavity 51 and aone-step stepped part 53 circumferentially formed in the boundary partbetween the minor diameter part 51 b and the major diameter part 51 a.The stepped part 53 is stepped so that the diameter is increased fromthe minor diameter part 51 b to the major diameter part 51 a. A slit 54is formed in the stepped part 53, and the slit 54 is circumferentiallyformed on the major diameter side (thick side) of the stepped part 53and allowed to communicate with the outside air.

The effect of this embodiment is described. In the resin molding metalmold 50 of this embodiment, as shown in FIG. 33, the molten resin 10,when injected from the gates 52 communicating with the minor diameterpart 51 b of the cavity 51, rises and falls on the minor diameter part51 b, flows to the lower major diameter part and upper major diameterpart 51 a of the cavity 51, and successively passes the stepped part 53and slit 54 formed in the circumferential direction of the minordiameter part 51 b to fill the major diameter part 51 a.

The molten resin 10 flowing from the minor diameter part 51 b of thecavity 51 to the major diameter part 51 a flows radially and flows intothe tooth part forming part 51 c.

The minor diameter part 51 b is formed so that the opening diameter isincreased with the stepped part 53 as the boundary to change the shapeof the shaft part 133 of the gear 130 of molded product from a thin partto a thick part. When the molten resin 10 flows from the thin part ofthe stepped part 53 to the thick part, its pressure is released due tothe presence of the stepped part 53 in the minor diameter part 51 b ofthe cavity 51 to weaken the force of pressing the molten resin 10 to thewall surface of the resin molding metal mold 50. Accordingly, anon-transfer part is apt to be formed in the edge part of the steppedpart 53 because the molten resin 10 is not sufficiently intrudedthereto. The non-transfer part is apt to start to induce a sink in thecooling process because its adhesive force to the resin molding metalmold 50 is smaller than that of the other part.

Since the slit 54 is formed in the stepped part 53, the molten resin 10flowing while closely fitting to the inner surface of the resin moldingmetal mold 50 by the fountain flow does not get into the edge parthaving the slit 54 formed thereon in the stepped part 53 as describedabove, and cannot get into the fine slit 54 when it flows on the slit54. Accordingly, the molten resin 10 moves in contact with the outsideair introduced from the slit 54 to generate a s ink ill the part facingthe stepped part 53 by the outside air introduced from the slit 54.

Accordingly, the sink can be selectively generated in the resin 10 partfacing the slit 54, and when the sink is once generated, this part isrelatively higher in temperature than the part making contact with theresin molding metal mold 50 because the cooling from the resin moldingmetal mold 50 is arrested, and also more easily moved because of the lowviscosity of the resin 10 to progress the sink.

This sink is progressed, whereby the part subjected to transfer is lesspulled to the thick part by this portion to prevent the sink orcontracting deformation of the transfer part.

As shown in FIG. 35, the slit 54 is formed in the resin molding metalmold 50 of the position forming a non-transfer part 134 of the moldedproduct 130, whereby the non-transfer part 134 can be formed in the partacing the slit 54 to improve the transfer property of the tooth part 131that is the transfer part, so that the shape precision of the moldedproduct 130 can be improved, and transfer of surface state such aswrinkle, transfer of fine surface shape or the like can be easily andprecisely performed.

In this embodiment, although the one-step stepped part 53 is formed onthe resin molding metal mold 50, for example, a two-step stepped part 55as shown in FIG. 36 or a stepped part having many steps may be formedwithout limiting the number of steps of the stepped part 53 to one toform the slit 54 on the stepped part 55. When a stepped part having aplurality of steps, for example, the two-step stepped part 55 is formed,the sink can be generated in the stepped part 55 in the same manner asdescribed above to form a non-transfer part 136 of a gear 135 as moldedproduct, as shown in FIG. 37, and also make the non-transfer part 136into a smooth shape.

FIGS. 38 and 40 show a sixth embodiment of the resin molding device,resin molding method and resin molded product of this invention, andFIG. 38 is a front sectional view of a resin molding metal mold 60according to the sixth embodiment of the resin molding device, resinmolding method and resin molded product of this invention.

This embodiment is applied to the same resin molding metal mold as theresin molding metal mold 1 of the first embodiment, and the samereference number is imparted to the same component as in the firstembodiment to omit the detailed description therefor.

In FIG. 38, the resin molding metal mold 60 that is the resin moldingdevice comprises a rib part 61 formed in the lower part of a flatplate-shaped cavity 2 and a plurality of gates 3 formed in the lowersurface central part of the rib part 61, and a molten resin 10introduced into the cavity 2 from the gates 3 through the rib part 61spreads and flows radially from the central rib part 61 of the cavity 2to fill the cavity 2.

A stepped part 62 is formed in the vicinity of the cavity 2 of the ribpart 61 in the circumferential direction of the rib part 61, and aplurality of steps is formed on the stepped part 62 as shown in FIGS. 38and 39. A slit 63 is formed in the first step of the stepped part 62.The slit 63 is circumferentially formed on the thick part side of thefirst step of the stepped part 62 and allowed to communicate with theoutside air.

The effect of this embodiment is described. In the resin molding metalmold 60 of this embodiment, as shown in FIG. 38, the molten resin 10,when infected from the gates 3 formed in the lower surface central partof the rib part 61, rises in the rib part 61 and successively passes thestepped part 62 and slit 63 formed in the circumferential direction ofthe rib part 61 to fill the cavity 2.

The rib part 61 is formed so that the opening diameter is graduallyincreased with the stepped part 62 having a plurality of steps as theboundary to change the shape of a molded product 140 (refer to FIG. 40)from a thin part to a thick part. When the molten resin 10 flows fromthe thin part to the thick part, its pressure is released over a widerange due to the presence of the stepped part 62 having a plurality ofsteps on the rib part 61 of the cavity 2 to weaken the force of pressingthe molten resin 10 to the wall surface of the resin molding metal mold60. Accordingly, a non-transfer part is apt to be formed in the edgepart of the stepped part 62 because the molten resin 10 is notsufficiently intruded thereto. The non-transfer part is apt to start toinduce a sink in the cooling process because its adhesive force to theresin molding metal mold 60 is smaller than that of the other part.

Since the slit 63 is formed on the stepped part 62, the molten resin 10flowing while closely fitting to the inner surface of the resin moldingmetal mold 60 by the fountain flow never gets into the edge part havingthe slit 63 formed thereon in the stepped part 62 as described above,and cannot get into the fine slit 63 when it flows on the slit 63.Accordingly, the molten resin 10 moves in contact with the outside airintroduced from the slit 63 to generate a sink over a wide range in thepart facing the stepped part 62 having a plurality of steps by theoutside air introduced from the slit 63.

Accordingly, the sink can be selectively generated over a wide range inthe resin 10 part facing the slit 63, and when the sink is oncegenerated, this part is relatively higher in temperature than the partmaking contact with the resin molding metal mold 60 because the coolingfrom the resin molding metal mold 60 is arrested, and also more easilymoved because of the low viscosity of the resin 10 to progress the sink.

This sink is progressed, whereby the part subjected to transfer is lesspulled to the thick part by this portion to prevent the sink orcontracting deformation of the transfer part.

As shown in FIG. 40, the stepped part 62 having a plurality of steps andthe slit 63 are formed in the resin molding metal mold 60 in theposition forming a non-transfer part 141 of the molded product 140,whereby the non-transfer part 141 is formed in the part facing thestepped part 62 and the slit 63 to improve the transfer property of atransfer part 142, so that the shape precision of the molded product 140can be improved, and transfer of surface state such as wrinkle, transferof fine surface shape or the like can be easily and precisely performed.

FIGS. 41-43 show a seventh embodiment of the resin molding device, resinmolding method and resin molded product of this invention, and FIG. 41is a front sectional view of a resin molding metal mold 70 according tothe seventh embodiment of the resin molding device, resin molding methodand resin molded product of this invention.

This embodiment is applied to the same resin molding metal mold as theresin molding metal mold 1 of the first embodiment, and the samereference number is imparted to the same component as in the firstembodiment to omit the detailed description therefor.

In FIG. 41, the resin molding metal mold 70 that is the resin moldingdevice comprises a rib part 71 formed in the lower part of a flatplate-shaped cavity 2 and a plurality of gates 3 formed in the lowersurface central part of the rib part 71, and a molten resin 10introduced into the cavity 2 from the gates 3 through the rib part 71spreads and flows radially from the central rib part 71 of the cavity 2to fill the cavity 2.

A stepped part 72 is formed in the vicinity of the cavity 2 of the ribpart 71 in the circumferential direction of the rib part 71, and thestepped part 72 comprises a plurality of steps and also a broad step 72as shown in FIGS. 42 and 43. An outside air inlet part 73 is circularlyformed in the broad step 72 a part of the stepped part 72 orthogonallyto the flowing direction of the molten resin 10 or circumferentially,and the outside air inlet part 73 is allowed to communicate with theoutside air through a communicating passage 73 opened to the outside ofthe resin molding metal mold 70 as shown in FIG. 41.

The outside inlet part 73 is formed of a porous member, at least onefine slit (clearance), or a movable member.

The effect of this embodiment is described. In the resin molding metalmold 70 of this embodiment, as shown in FIG. 41, the molten resin 10,when injected from the gates 3 formed in the lower surface central partof the rib part 71, rises in the rib part 71 and successively passes thestepped part 72 and outside air inlet part 73 formed in thecircumferential direction of the rib part 71 to fill the cavity 2.

The rib part 71 is formed so that the opening diameter is graduallyincreased with the stepped part 72 having a plurality of steps as theboundary to change the shape of a molded product 150 (refer to FIG. 43)from a thin part to a thick part. When the molten resin 10 flaws fromthe thin part to the thick part, its pressure is released over a widerange due to the presence of the stepped part 72 consisting of aplurality of steps in the rib part 71 of the cavity 2 to weaken theforce of pressing the molten resin 10 to the wall surface of the resinmolding metal mold 70. Thus, a non-transfer part is apt to be formed inthe edge part of the stepped part 72 because the molten resin 10 is notsufficiently intruded thereto. The non-transfer part is apt to start toinduce a sink in the cooling process because its adhesive force to theresin molding metal mold 70 is smaller than that of the other part.

Since the outside air inlet part 73 is formed in the broad step 72 a ofthe stepped part 72, the molten resin 10 flowing while closely fittingto the inner surface of the resin molding metal mold 70 by the fountainflow does not get into the edge part having the outside air inlet part73 formed thereon in the stepped part 71 as described and causes a sinkin a wide range in the part facing the stepped part 72 having aplurality of steps by the outside air introduced in the outside airinlet part 73 when it flows on the outside air inlet part 73.

Accordingly, the sin can be selectively generated over a wide range inthe resin 10 part facing the outside air inlet part 73, and when thesink is once generated, this part is relatively higher in temperaturethan the part making contact with the resin molding metal mold 70because the cooling from the resin molding metal mold 70 is arrested,and also more easily moved because of the low viscosity of the resin 10to progress the sink.

This sink is progressed, whereby the part subjected to transfer is lesspulled to the thick part by this portion to prevent the sink orcontracting deformation of the transfer part.

Accordingly, the stepped part 72 consisting of a plurality of steps andthe outside air inlet part 73 are formed on the resin molding metal mold70 in the position forming a non-transfer part 151 of the molded product150 as shown in FIG. 43, whereby the non-transfer part 151 can be formedin the part acing the stepped part 72 and outside air inlet part 73 toimprove the transfer property of a transfer part 152, so that the shapeprecision of the molded product 150 can be improved, and transfer ofsurface state such as wrinkle, transfer of fine surface shape or thelike can be easily and precisely performed.

In each of the embodiments described above, non-transfer parts ofvarious shapes 161-164, for example, can be formed on a molded product160 as shown in FIGS. 44-47 by variously changing the shape of thestepped part. FIG. 44 shows, for example, a non-transfer part 161 of themolded product 160 formed by using a resin molding metal mold having aone-step stepped part changed at a right angle from a minor diametershape to a major diameter shape in the flowing direction (the arroweddirection in FIG. 44) of the molten resin 10 and a slit, and introducingthe outside air thereto by an outside air feeding machine from the slitduring and after the injection of the resin. FIG. 45 shows anon-transfer part 162 of the molded product 160 formed by using a resinmolding metal mold having a one-stepped part changed at a right anglefrom a minor diameter shape to a major diameter shape in the flowingdirection (the arrowed direction in FIG. 45) of the molten resin 10 anda slit, and introducing the outside air thereto by the outside airfeeding machine after the injection of the resin. FIG. 46 shows anon-transfer part 163 of the molded product 160 formed by using a resinmolding metal mold having a multi-step stepped part changed in a taperedshape from a minor diameter shape to a major diameter shape in theflowing direction (the arrowed direction in FIG. 46) of the molten resin10 and a slit, and introducing the outside air thereto by the outsideair feeding machine during and after the injection of the resin. FIG. 47shows a non-transfer part 164 of the molded product 160 formed by usinga resin molding metal mold having a multi-step stepped part changed in atapered shape from a minor diameter shape to a major diameter shape inthe flowing direction (the arrowed direction in FIG. 47) of the moltenresin 10 and a slit, and introducing the outside air thereto by theoutside air feeding machine after the injection of resin.

Although the slit or outside air inlet part is formed in the steppedpart in each of the above-mentioned embodiments, only a slit 80 or onlyan outside air inlet part may be provided as shown in FIGS. 48 and 49without providing any stepped part. In this case, since the molten resin10 injected into the cavity 2 is cooled with the outside air introducedfrom the slit 80 while passing in the slit 80 part as shown in FIGS. 48and 49, a sink can be selectively generated in the part of the slit 80.When the gas feeding machine connected to the slit 80 or the outside airinlet part is driven during the filling of the molten resin 10 tointroduce the gas into the cavity 2, particularly, the resin 10 of thepart facing the slit 80 or outside air inlet part can be made hardlyfitted to the metal mold surface. Accordingly, the resin of this part iseasily separated from the metal mold surface to facilitate the formationof sink in the cooling process. The transfer property of the transfersurface can be improved further more by enlarging the sink of this partmore.

Although this invention is specifically described so far on the basis ofthe preferred embodiments, this invention can be, of course, variouslychanged without being limited by the above embodiments.

1. A resin molding method for molding a resin molded product byinjecting a molten resin into the cavity of a metal mold followed bysolidification, the method comprising: providing a stepped part whichchanges a molded product shape from a thin part to a thick part in saidcavity; providing an outside air inlet part which is formed on saidmetal mold and is opened to said stepped part in said cavity or an innerwall of said cavity which forms said thick part of said molten resin toallow an outside of said metal mold to communicate with an interior ofsaid cavity; injecting said molten resin into said cavity so as to floworthogonally to said stepped part to form said thin part to said thickpart of said molten resin with said stepped part as a boundary; andforming sinks on said molten resin by being in contact with an outsideair via said outside air inlet part.
 2. A resin molded product moldingmethod according to claim 1 wherein said outside air inlet part isformed in said stepped part or the boundary of steps of the steppedpart.
 3. A resin molding method according to claim 1 wherein saidstepped part is formed so as to have a plurality of continuous steps. 4.A resin molding method according to claim 1 wherein said stepped part isformed so as to have a plurality of continuous steps, and said outsideair inlet part is formed in the state communicating with said cavity inthe area between the steps.
 5. A resin molding method according to claim1 wherein a prescribed gas is fed into said cavity through said outsideair inlet part by a gas feeding device configured to forcedly feed saidgas to said outside air inlet part during and after the injection ofsaid molten resin into said cavity.
 6. A resin molding method accordingto claim 1 wherein a prescribed gas is fed into said cavity through saidoutside air inlet part by a gas feeding device configured to forcedlyfeed said gas to said outside air inlet part after the injection of saidmolten resin into said cavity.
 7. A resin molding method according toclaim 1, further comprising: forming a non-transfer part in said outletair inlet part.
 8. A resin molding method according to claim 2, furthercomprising: forming a non-transfer part in said stepped part or theboundary of steps of the stepped part.
 9. A resin molding methodaccording to claim 1, further comprising: using a metal mold having atooth-shaped recessed part for molding a tooth part of a gear, andforming said tooth part in said tooth-shaped recessed part.
 10. A resinmolding method for molding a resin molded product by injecting a moltenresin into the cavity of a metal mold followed by solidification, themethod comprising: providing a stepped part which changes a moldedproduct shape from a thin part to a thick part in said cavity; providinga slit which is formed on said metal mold and is opened to said steppedpart in said cavity or an inner wall of said cavity which forms saidthick part of said molten resin to allow an outside of said metal moldto communicate with an interior of said cavity; injecting said moltenresin into said cavity so as to flow orthogonally to said stepped partto form said thin part to said thick part of said molten resin with saidstepped part as a boundary; and forming sinks on said molten resin bybeing in contact with an outside air via said slit.
 11. A resin moldedproduct molding method according to claim 10 wherein said slit is formedin said stepped part or the boundary of steps of the stepped part.
 12. Aresin molding method according to claim 10 wherein said stepped part isformed so as to have a plurality of continuous steps.
 13. A resinmolding method according to claim 10 wherein said stepped part is formedso as to have a plurality of continuous steps, and said slitcommunicates with said cavity in the area between the steps.
 14. A resinmolding method according to claim 10 wherein a prescribed gas is fedinto said cavity through said slit by a gas feeding means for forcedlyfeeding said gas to said slit during and after the injection of saidmolten resin into said cavity.
 15. A resin molding method according toclaim 10 wherein a prescribed gas is fed into said cavity through saidslit by a gas feeding means for forcedly feeding said gas to said slitafter the injection of said molten resin into said cavity.
 16. A resinmolding method according to claim 10, further comprising: forming anon-transfer part in said slit part.
 17. A resin molding methodaccording to claim 11, further comprising: forming a non-transfer partin said stepped part or the boundary of steps of the stepped part.
 18. Aresin molding method according to claim 10, further comprising: using ametal mold having a tooth-shaped recessed part for molding a tooth partof a gear, and forming said tooth part in said tooth-shaped recessedpart.